1. Field of the Invention
The present invention relates to a microscope illuminating apparatus used in, e.g., a system microscope.
2. Description of the Related Art
Conventionally, in a system microscope in which an attachment and various types of optical members are present in its observation optical system in accordance with the content of microscopic observation, an infinity correction observation optical system is used so that the optical members do not adversely affect the magnification and the image forming characteristics.
FIG. 24 shows a reflected illuminating apparatus applied to a system microscope having an infinity correction observation optical system.
Referring to FIG. 24, an objective lens 1 is mounted on a revolver 2 of the microscope through an objective lens outer frame 1a. An objective lens system 3 constituting part of the infinity correction observation optical system is provided at the central portion of the objective lens 1. A lens frame 3a for separating dark field illumination light and bright field illumination light is provided on the outer circumference of the objective lens system 3. An annular condenser lens 4 is provided on the outer circumference of the distal end portion of the objective lens system 3. An annular mirror 5 having a hole for deflecting illumination light toward the condenser lens 4 is arranged above the objective lens system 3. A light-shielding tube 6 is arranged at the central portion of the holed mirror 5 to be coaxial with the observation optical axis. The light-shielding tube is arranged to prevent annular illumination light from mixing in the observation optical path. Light emitting from a light source 7 is collimated to illumination light comprising parallel rays by illumination lenses 8 to 10 and is incident on the holed mirror 5. Since the optical members, e.g., an attachment and the half mirror described above are interposed between the objective lens system 3 and the light-shielding tube 6, a sufficient distance is set between the objective lens system 3 and the light-shielding tube 6. A light-shielding tube 12 for separating an illumination optical path and the observation optical path is provided between the objective lens system 3 and the light-shielding tube 6.
The objective lens system 3 described above apparently serves as a condenser lens during reflected bright field illumination.
In the reflected illuminating apparatus having the above arrangement, the illumination light emitted from the light source 7 is set to parallel illumination light by the illumination lenses 8 to 10 and is incident on the holed mirror 5. Annular illumination light reflected by the holed mirror 5 is incident on the annular condenser lens 4 through the illumination optical path and is condensed on an object surface O. Light reflected by the object surface O is incident on a focusing lens (not shown) through the objective lens system 3 and the light-shielding tube 6. When the light reflected by the object surface O passes through the light-shielding tube 6, generation of flare in the light-shielding tube 6 is prevented by a stop 11 provided in the light-shielding tube 6.
In the reflected illuminating apparatus described above, however, the numerical aperture must be set large to improve the resolution of the objective lens system 3 and the distance between the objective lens system 3 and the stop 11 must be set long to interpose the attachment in the observation optical system. This leads to a lack in quantity of light around the observation field.
This problem will be discussed with reference to FIG. 25. Note that FIG. 25 schematically shows the infinity correction observation optical system between the object surface O and the stop 11 of the light-shielding tube 6.
In the infinity correction observation optical system in FIG. 25, the ray of light emitting from a center P2 of the observation field propagates in parallel with the optical axis, as indicated by .nu.1 to .nu.3, while the ray of light emitting from a periphery P1 of the observation field propagates obliquely to the optical axis, as indicated by .nu.4 to .nu.6. Therefore, if the stop 11 is present halfway, although the ray from the center P2 of the observation field is entirely transmitted through it, the rays from the periphery P1 from the observation field may be cut by the stop 11, and the farther from the center of the observation field, the larger the attenuation amount of the quantity of light, resulting in a dark image. This tendency becomes strong as the stop position becomes farther as from a to b. A similar lack in quantity of light also occurs when the numerical aperture of the objective lens is increased.
This lack in quantity of light can be solved to a certain degree by widening the observation optical path. In the conventional reflected illuminating apparatus, however, since the annular illumination optical path and the observation optical path are separated by the light-shielding tube 12 in order to prevent mixing of the illumination light in the observation optical path, the width of the observation optical path is limited, and it is difficult to widen the observation optical path.
Optical microscopes are widely utilized in the field of biology as they can observe a live specimen. Above all, a dark field microscope has the features of the optical microscope while it has a resolving power greatly higher than that of the optical microscope. The dark field microscope can thus detect a very small molecule, e.g., a molecule having a size of several tens of nm and is effective in examining the dynamic behavior of, e.g., various small molecules constituting a small organ in a cell.
FIG. 26 shows an illuminating apparatus of a conventional transmitted dark field microscope having an arrangement as follows.
A stage 63 for placing a specimen 62 thereon is supported on a microscope frame 61 to be movable along an observation optical axis 64. An objective lens 65 for enlarging and observing the specimen 62 is fixed above the frame 61 along the observation optical axis 64. A lamphouse 67 housing an illumination light source 66 is fixed below the frame 61. A beam emitted from the light source 66 is guided to a reflecting mirror 71 through a plurality of filters 69 and a field stop 70 sequentially, and the beam reflected by the reflecting mirror 71 is guided toward the specimen 62.
The filters 69 can be inserted in and removed from the illumination optical path in order to adjust the brightness of the illumination light source 66 and the nature of the light, e.g., color.
The arrangement described above is the same as that of an ordinary microscope for transmitted illumination field observation. In addition to this arrangement, the dark field microscope needs a dark field condenser 72 as follows. That is, the dark field condenser 72 must be constructed so that it has a numerical aperture larger than that of the objective lens 65 and can illuminate the specimen 62 such that the illumination light will not be directly incident on the objective lens 65 and such that only the light scattered by the specimen 62 is incident on the objective lens 65.
For this purpose, the dark field condenser 72 has an annular condenser case 73, a dark field condenser lens 74 fixed on the end portion of the aperture of the condenser case 73 and having first and second spherical reflecting surfaces 74a and 74b, and a ring slit 75 fixed inside the condenser case 73 to be close to the condenser lens 74. The dark field condenser 72 having this arrangement is supported by and fixed on a condenser carrier 76 which is supported to be movable along the observation optical axis 64 and adjustable in the vertical direction with respect to the observation optical axis 64. The condenser carrier 76 is mounted on the stage 63.
Thus, the illumination light emitted from the illumination light source 66 passes through the ring slit 75 to become annular, is directed outward by the first reflecting surface 74a of the dark field condenser lens 74, and is then directed inward by the second reflecting surface 74b of the condenser lens 74. As a result, the illumination light is not directly incident on the objective lens 65 but is radiated on the specimen 62. In this case, of the transmitted bright field beams, only the beam which has passed through the ring slit 75 serves as the dark field illumination beam.
This dark field microscope has problems as follows:
(1) Since only the beam, of the illumination beams, that has passed through the ring slit 75 serves as the dark field illumination beam, the illumination efficiency is very low, and accordingly the dark field illumination becomes very dark. PA1 (2) To perform switching between the dark field illumination and the bright field illumination, the entire dark field condenser 72 must be exchanged, and after the exchange, optical adjustment of the condenser 72, i.e., centering of the specimen 62 and adjustment of the distance between the specimen 62 and the condenser lens 74 must be performed every time illumination is switched. PA1 (3) The beam passing through the ring slit 75 of the condenser 72 for the dark field illumination is the beam emerging from the periphery of the field stop 70, and in dark field observation, an operation for aperturing the field stop 70 needs to be performed. PA1 (4) Since the quantity of light to be observed is largely changed after switching between the dark field the and bright field, the filters 69 for brightness control must be inserted or removed.
A microscope illuminating apparatus from which the problem (1) is solved is conventionally known, as described in Published Unexamined Japanese Patent Application No. 55-140811.
This microscope illuminating apparatus has a light source remote from a precious stone to be examined, a glass fiber optical guide member extending to an annular endpiece, and a reflecting mirror mounted on the endpiece, and has a function as follows. That is, light emitted from the light source is gathered by the glass fiber bundle. The fiber constituting the bundle is dispersed in the endpiece so as to transmit the annular light to the upper surface of the endpiece. Light emerging through the endpiece is focused by the reflecting mirror and is radiated on the precious stone.
Hence, although this known example can prevent dark field illumination of problem (1), the remaining problems (2), (3), and (4) cannot be solved.
Recently, in reflected dark field observation, a method having an optical fiber bundle in order to perform illumination having a small variation with a large illuminance is disclosed in the specification of Japanese Patent Application No. 3-77881. According to this method, an annular optical fiber 100 is detachably formed on a revolver 101, and light emerging from the optical fiber 100 is supplied to an objective lens 102 as dark field illumination light, as shown in FIGS. 27 and 28. Light-shielding tubes 103a and 103b for separating the dark field illumination light and the observation light are fixed in the revolver 101 and the objective lens 102, respectively, by three stays 104a, 104b, and 104c shown in FIG. 28.
Two end portions D and F of each of the three stays 104a, 104b, and 104c are arcuatedly formed, as shown by the stay 104a, and a central portion E connecting the two end portions D and F is linearly formed. As a result, when the illumination light is radiated on these linear portions, diffracted light is emerged from these portions. Because of the diffracted light and the shadows of the stays, the illumination light passing through the stays forms fringes of brightness and darkness. When a microscopic picture of reflected dark field observation is taken under this illumination light, especially in the case of high-magnification observation, a shag 108 is found at, e.g., an edge 107 portion of a pattern 106 of a silicon wafer 105, as shown in FIG. 17. As a result, it is difficult to observe a smaller object from an observation image or a picture with high accuracy.